Conrad and Hock, Formaldehydderivate der Urethane, Berichte, 36, 2206 (1903) disclose the condensation reaction of formaldehyde and the ethyl ester of carbamic acid or urethane to produce methylene diurethane (MEDU), a compound of the formula ##STR1##
Sasaki et al., J. Org. Chem., 37, 14 (1972), disclose that norbornadiene can be heated in benzene solution with methylenebisurethane in the presence of boron trifluoride etherate to produce a mixture of carbamates including the tricyclic ethyl ester ##STR2## There is no suggestion however, that the tricyclic ethyl ester or any other ester can be cracked to yield useful tricyclic diisocyanates.
It has been discovered now that diisocyanate norbornyl derivatives can be prepared using inexpensive starting materials, for example norbornadiene, formaldehyde and methyl carbamate to produce novel norbornyl carbamates. These novel carbamates can in turn, be cracked to yield new and useful diisocyanate norbornyl derivatives, heretofore unobtainable in this way from the prior art. The novel products lack many of the disadvantages of the prior art. In particular, they have high reactivity, light stability and selectivity.